Most mitochondrial components, including proteins, lipids and smaller molecules, are produced outside the organelle and must be imported through one or both of the mitochondrial membranes to support development of the organelle. This project studies the assembly of the mitochondrial ATPase which is comprised of subunits made both inside and outside the organelle. The project also concerns the synthesis of two other proteins imported from the cytosol citrate synthase and manganese superoxide dismutase - two enzymes whose synthesis is controlled by the extracellular environment. We will concentrate on three aspects of the problem of mitochondrial biogenesis: (1) the assembly of the enzyme complex from imported subunits and subunits made on mitochondrial ribosomes; (2) proteins in the mitochondrion which mediate protein import into mitochondria; and (3) regulation of nuclear gene expression involved in catabolite repression and oxygen adaptation of mitochondrial enzymes. Specifically, the project entails: (A) Studying the import and assembly of the ATPase in a cell-free system using mitochondria from wild-type and mutant yeast cells. (B) Selecting and characterizing mutations which affect the ability of mitochondria to take up proteins. (C) Isolating genes for citrate synthase, Mn-superoxide dismutase, and specific ATPase subunits, determining their structures and generating mutations in them. (D) Characterizing more completely mutations which we have already described which seem to alter the interactions between the nuclear and mitochondrial encoded subunits of the ATPase complex. This work employs the yeast Saccharomyces cerevisiae because it has mitochondria functionally in distinguishable from those of mammalian cells and, as a facultative anaerobe, permits the isolation of mutants which are deficient in respiration. Our object is to use mitochondria as a model system for the study of the molecular biology of membranes. Understanding these basic processes of cell biology has significance for the study of cancer and metabolic disease.